Evidence of several internal projects at Valve including Half-life 3, Left 4 Dead 3, Source 2 and many others have been discovered from a mailing list found within project management and bug tracking software, Jira.

Valve were recently forced to react to an issue with Jira. A metaphorical window was left open which allowed people to publicly access Valve's internal tickets. Valve were quick to shut down public access to their Jira database, so we recommend you don't attempt to access it.